The present invention relates to a coating apparatus for coating a liquid agent such as a resist solution and an anti-reflection film coating (ARC) solution on a substrate such as semiconductor wafer and an LCD substrate.
In a manufacturing process for a semiconductor device, usually a photographic technology is used. In the photolithographic technology, a resist is first coated over a surface of the semiconductor wafer, exposed to light to form a predetermined pattern, and subjected to a developing step. In this manner, the resist film having a predetermined pattern is formed on the wafer. The resultant substrate is further subjected to a film formation step and an etching step to form a circuit having a predetermined pattern. The series of resist processing treatments are usually performed in a coating/developing system disclosed in U.S. Pat. No. 5,664,254.
At present, mostly used as the method for coating the resist solution over a wafer is a spin-coating method. In the spin coating method, a resist solution is pumped up from a tank, filtrated by a filter, and spurted out from a nozzle toward the wafer W by way of an operate valve. Since the wafer W is spin-rotated while being held by a spin chuck, the resist solution is spread swiftly over the entire wafer surface by centrifugal force, thereby forming a resist film having a uniform thickness.
However, there is a problem with the conventionally used coating apparatus; when the resist solution is spurted out from the pump toward the filter, particles and a gelatinized resist solution which have been captured by the filter are removed from the filter by spurting pressure. These removed materials sometimes attach to the wafer. In particular, when a large amount of the resist solution is spurted out in one time, impact of the spurting current upon the filter becomes large. It follows that the captured materials are likely to remove from the filter to generate defects in the coating film of the substrate. The occurrence rate of the defects of the coated film increases with an increase in size of the substrate, decreasing the yield of the device.
Recently, a wafer size tends to increase and a device circuit has been miniaturized. With this tendency, a low-viscosity resist solution and low-viscosity anti-reflection coating film solution (hereinafter referred to as "ARC solution") containing a surfactant have been increasingly used. However, there are problems when the low-viscosity coating solution is used; bubbles are likely to generate in the coating solution passed through a filter when it spurts out. If the coating solution containing bubbles is supplied to the wafer, defects may be generated in the formed coating film.